Anesthetic vaporizers have been proposed wherein the gas (or air) inflow to the vaporizer unit is proportionately divided between a path through the vaporizing chamber containing the anesthetic liquid, and a path bypassing the chamber so that the mixture at the vaporizer outlet represents a desired concentration of the anesthetic according to patient requirement. Since operation of the vaporizer results in heat extraction from the chamber, a temperature compensating valve, generally in the outlet passage of the chamber, is usually provided to increase proportionate flow through the chamber as the vaporization rate decreases with decrease in chamber temperature.
The prior art devices for the most part have not been entirely satisfactory in overcoming certain technical problems, such as maintaining the selected concentration of anesthetic substantially constant irrespective of changes in the flow rate of the gas and/or the temperature of the vaporizer chamber within preselected ranges of gas flow and chamber temperature. Another problem is involved in the operation of multiple controls for making full use of the vaporizer, that in turn generally results in a more complex and costly structural design.
A vaporizer unit constituting an improvement over prior art devices in precision control of the selected anesthetic concentration, is disclosed in U.S. Pat. No. 3,841,560 granted Oct. 15, 1974 to Ulrich Sielaff and assigned to the same assignee as the present invention. The present invention is an improvement thereon, especially as to incorporation of all manual control functions in a single rotary valve assembly, a simplified temperature compensation bypass, and other features that are described herein.